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MEI Online: Biotechnology: Latest News: December 10th 2008

 
 

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:: Bioleaching Plant Proposed for Cobalt

BacTech Mining Corporation, a Toronto-based company, has signed a memorandum of understanding with Gold Bullion Development Corp. of Cobalt to investigate the feasibility of using BacTech's proprietary bioleaching technology to process tailings from the Castle Mine in Gowganda, 50 kilometres west of Cobalt. BacTech has already started to raise funds for a $20 million pilot plant in Cobalt that could be expanded to process some 16 to 18 million tonnes of tailings resulting from silver mining activities between 1903 and 1922.

The tailings, deposited on surface and in lakes, pose an environmental problem because of high concentrations of arsenic, but they also contain economically significant values of silver and cobalt. "During a span of 25 years, the Cobalt camp produced more than 300,000 ounces of silver," said Ross Orr, president and CEO of BacTech. "Most of the cobalt was disposed of because there were very few applications for it prior to World War Two and, because they were mining high-grade silver veins, they left the tougher silver in the sulphides behind along with the nickel, which wasn't high enough grade to go after. "Over 100 years, a lot of the arsenic has been mobilized and has leached into local lakes to the point where the government has posted no swimming or fishing signs, so it's a real problem." Crosswise Lake in Cobalt used to be 40 metres deep, said Orr. Now, it's only seven metres deep. "They just threw everything into the lakes. They threw it on land. It's quite something. A lot of the sulphides have not oxidized because they're hosted in water, but there is arsenic leaching out."

The BacTech bioleaching process will liberate the iron and arsenic in the tailings and bind them together as iron arsenate, a benign Environmental Protection Agency-approved product that could be disposed of safely, said Orr. "The fact that we have decent grades of silver, cobalt and nickel in the concentrate makes this an environmental cleanup that actually makes money." Assays conducted following gravity separation of a test sample from Gold Bullion's Castle Mine tailings showed grades of 245.25 ounces per ton of silver, 2.12 per cent cobalt and 12.64 per cent arsenic. Arsenic levels

The press release reporting arsenic levels of 12 per cent caught Orr's attention and prompted him to contact Gold Bullion president Frank Basa. "I knew that no smelter or roaster would treat that," he said. BacTech's bioleaching technology was developed in the late 1980s at King's College in London, England by scientists who were interested in finding a way to extract sulphur from coal. According to Orr, "a couple of sharp Australians" learned about their work and said, "Forget about coal. This will work for gold." The technology migrated to Perth, Australia in the early '90s and ended up in Toronto in 1997 to gain access to the North American capital markets.

Three bioleaching plants using BacTech technology have been built to date. The first plant, currently idle due to low ore grades, was built in 1994 at the Youanmi Mine in Western Australia. The second one was commissioned in 1997 at the Beaconsfield Mine in Tasmania and the third was built in China in 2000. In all three cases, BacTech licensed the technology and "sat back and watched someone else make all the money," said Orr.

The company's current strategy is to take an equity position in projects. In June, for example, Orr reached an agreement with Yamana Gold to acquire its 33 per cent stake in two refractory gold projects in Papua New Guinea. In return, Yamana acquired a 19.97 per cent stake in BacTech.

In 2001, BacTech successfully tested its technology on base metal ores on behalf of Penoles of Mexico. A $5 million demonstration plant in Monterrey proved the viability of using bioleaching technology to treat extremely refractory copper Chalpopyrite containing smelter penalty elements, including arsenic. There are approximately 20 bioleaching plants in the world, most of them built by Gold Fields Limited, which sold its Biox technology business to Bateman Engineering for $8.84 million in October.

The bioleaching process is conducted in a series of stirred, aerated stainless steel tanks. Oxidation of the sulphides occurs as the pulp progresses through the series of tanks over a period of four to six days. Heap leaching, by contrast, takes between six and 12 months. "The bacteria derive their energy by eating sulphides," explained Orr. "They don't care about the gold. They don't care about the iron. They don't care about the arsenic. They eat away at the sulphides and that spins off the other elements."

The most likely scenario for Cobalt would be to set up a flotation circuit at the site of a tailings deposit, separate out the sulphides and truck the concentrate to a central bioleach plant in Cobalt. $20 million

BacTech hopes to tap into various Canadian sustainability funds to finance half of the $20 million cost of a pilot plant and would split the difference with Gold Bullion. The pilot plant would treat 200,000 tonnes of tailings per year, and could be expanded to treat one million tonnes once the technology is proven to be feasible. "The bioleach component of the Cobalt project is not the issue," said Orr. "The big questions are how to capture as much of the concentrate as possible from the tailings, what the end product is, what we do with it and who's going to buy it."

A 500 kilogram sample of Castle Mine tailings was shipped in September to SGS Lakefield to provide assay and mineralization analysis and to identify appropriate pre-concentration methods to maximize metal recovery. The resulting concentrate will then be sent to SGS Oretest in Perth where it will be subjected to a series of bioleaching amenability tests.

Bioleaching is much more environmentally friendly than traditional smelting, said Orr. "The world's going away from burning. That's the bottom line." BacTech hopes to have the Cobalt plant up and running by 2010.

 

 

   

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